1. Field of the Invention
The present invention relates generally to a valve that is used to regulate the flow of fluid. In one particular application, the invention relates to a valve that is used in systems designed to drain fluid from the thoracic cavity.
2. Description of the Related Art
A number of fluid recovery systems have been developed for withdrawing fluid, such as air and/or blood, from a person after chest surgery or trauma. Such systems are intended to remove fluid from the pleural space or the mediastinal cavity and restore the vacuum (sub-atmospheric pressure) that is normally present in the pleural space. The systems are usually adapted to allow suction to be applied to the chest cavity to facilitate, among other things, the removal of the blood from the pleural space. Once the fluid has been removed, the pleural membrane is allowed to heal and the normal condition of the pleural space is restored.
Various drainage devices, of varying complexity, have been developed for the above-mentioned purpose of draining fluids from either the pleural or mediastinal space. These devices typically include a housing that contains a number of chambers to collect fluid from the pleural space. In addition to the chambers, the housing contains a number of components such as valves and ports that may be manufactured separately and then attached to the housing. Typical drainage devices must accomplish drainage by allowing air to flow from the chest and through the chest drain without allowing air to flow back into the chest cavity. Second, there must be some protection against positive pressure so that the lung cavity is not subjected to positive pressure. Since the physiologically normal pressure of the pleural space is between −3 and −8 cm of water, any positive pressure within the pleural space is abnormal and can be very dangerous. Finally, the lung cavity must be protected from excessive negative pressure. If the pressure in the lung cavity falls below a predetermined minimum (i.e., excessive sub-atmospheric pressure) lung tissue can be damaged and sutures could become dislodged which could lead to bleeding. A suitable chest drain protects a patient by preventing the reverse flow of air back into the lung cavity within a given range, preventing positive pressure in the lung cavity and preventing excessive sub-atmospheric pressure in the lung cavity.
A one-way valve is used to allow fluid to flow from the chest to the collection device and prevent the reverse flow of air back into the lung. This one-way valve may be mechanical or water-based. When the one-way valve is water-based, it usually takes the form of a U-tube in which water is disposed on the bottom. Such a water-based one-way valve is usually called a water seal. The water seal protects the patient from excessive sub-atmospheric pressure by allowing air pressure to equalize by the flow of air back into the collection chamber (and the lung cavity) if the lung cavity develops excessive sub-atmospheric pressure.
Various persons have suggested the replacement of the water seal with a mechanical one-way valve that would prevent the reverse flow of air back to the patient. The inclusion of a mechanical one-way valve provides advantages because water would not be necessary for the device to operate. However, the inclusion of a mechanical one-way valve has required the incorporation of a specific so-called “negative pressure relief valve” so the patient can be protected from excessive sub-atmospheric pressure. Nearly all typical devices include a positive pressure relief valve that protects a patient from positive pressure.
The design of the one-way valve for use in a chest drainage device poses engineering challenges because the valve should open at a very slight pressure difference between the upstream side and the downstream side of the valve. Additionally, a valve used in a chest drainage system should allow for significant flow of air through the device. The designs must also be cost effective. In an era of cost containment for healthcare, devices that have fewer, simpler parts can be manufactured less expensively than a device with many parts. Accordingly, there is a need for a chest drainage device with fewer working parts that can be inexpensively produced. Additionally, there is a need for a single valve which can perform multiple functions.